1. Field of the Invention
The invention relates to a radiation-sensitive resin composition, a method for forming a resist pattern, a polymer, and a polymerizable compound.
2. Discussion of the Background
In the field of micro fabrication such as production of integrated circuit devices, a fine resist pattern may be formed by forming a resist film on a substrate using a resin composition including an acid-labile group-containing polymer, exposing the resist film by applying short-wavelength radiation (e.g., excimer laser light) to the resist film via a mask pattern, and removing the exposed area by alkali development. This process may utilize a chemically-amplified resist that includes a radiation-sensitive acid generator that generates an acid upon irradiation, and exhibits improved sensitivity due to the acid.
Liquid immersion lithography has become widespread as a method that can form a finer resist pattern (line width: about 45 nm, for example). According to this process, exposure is conducted in a state in which the exposure optical path (i.e., the space between the lens and the resist film) is filled with an immersion liquid (e.g., purified water or fluorine-containing inert liquid) that has a refractive index (n) higher than that of air and inert gas. Therefore, the depth of focus decreases to only a small extent, and high resolution can be obtained even when increasing the numerical aperture (NA) of the lens.
A resin composition that contains a fluorine-containing polymer that exhibits high hydrophobicity has been proposed as resin composition used for liquid immersion lithography aimed at preventing elution of the acid generator or the like from the resist film into the immersion liquid, and providing the resist film with improved water repellency (see WO2007/116664A).
A fluorine-containing polymer that exhibits hydrophobicity during liquid immersion lithography, and exhibits hydrophilicity during alkali development, specifically a fluorine-containing polymer in which a fluoroacyl group that exhibits high hydrophobicity is introduced into a phenolic hydroxyl group) has also been proposed aimed at suppressing development defects or the like in the unexposed area due to hydrophobization of the resist film (see Japanese Patent Application Publication (KOKAI) No. 2009-132843 and Japanese Patent Application Publication (KOKAI) No. 2009-139909).
The fluorine-containing polymer disclosed in Japanese Patent Application Publication No. 2009-132843 or Japanese Patent Application Publication No. 2009-139909 exhibits hydrophobicity during liquid immersion lithography due to the fluoroacyl group, and exhibits hydrophilicity during alkali development due to the phenolic hydroxyl group via elimination of the fluoroacyl group. Therefore, occurrence of development defects in the unexposed area is expected to be suppressed.
The fluorine-containing polymer disclosed in Japanese Patent Application Publication No. 2009-132843 or Japanese Patent Application Publication No. 2009-139909 may suppress occurrence of development defects in the unexposed area to some extent.